Patent GB-631699-A (GB)
Title: A process for the production of cyclohexane
IPC: C07C13/18
Filed: 1947-06-17
Abstract: Cyclohexane is separated from admixture with benzene by fractional distillation in the presence of normal hexane and/or methylcyclopentane.  A ratio of normal hexane and/or methylcyclopentane to benzene of at least 10 to 1, preferably 15 to 1, by volume is maintained.  Preferably all components are derived from a straight run naphthenic gasoline feed (see Group IV (b)).ALSO:Cyclohexane substantially free from benzene is obtained when methylcyclopentane admixed with benzene is isomerized to cyclohexane and the resultant mixture is fractionated together with hydrocarbons selected from normal hexane and methylcyclopentane to give the said cyclohexane and a fraction comprising methylcyclopentane and/or open chain hexanes and benzene.  The hydrocarbons are added to effect an efficient separation of benzene from cyclohexane and preferably normal hexane is built up within the reaction system so that the separation is complete by, e.g., fractionating a naphthenic straight-run gasoline feed to obtain a methylpentane fraction and a methylcyclopentanebenzene fraction, the former being isomerized to normal hexane and the latter to cyclohexanebenzene mixture when the two isomerisates are combined and are fractionated in a product zone.  Catalysts for the isomerization of methylcyclopentane specified are metal halides of the Friedel-Crafts type, particularly aluminium halides such as the chloride or bromide, organoaluminium halide complexes, preferably a preformed aluminium chloride hydrocarbon complex, and molten salt type catalysts such as aluminium chloride admixed with one or more halide salts.  Temperatures instanced are from 20 DEG  to 150 DEG C., preferably 50 DEG  to 95 DEG  C.  Hydrogen halide promoters, e.g. hydrogen chloride, are preferably present in amounts of 0.1 to 5 per cent, preferably below 1 per cent.  It is preferred that any normal hexane present in this stage of the process remains unaffected by the isomerization conditions employed as by, e.g. using organo-metal halide type catalysts at below 80 DEG  C., or the spent or partly-spent catalysts from the methyl pentane isomerization stage. Catalysts for the isomerization of methyl pentanes instanced are heavy metal sulphides, particularly those derived from metals of the left-hand side of Group 6 of the Periodic Table, e.g. molybdenum and/or tungsten sulphide, and may be combined with an inert diluent or support such as aluminium oxide.  Temperatures instanced are 300 DEG  to 600 DEG  C., preferably 350 DEG  to 450 DEG  C. and hydrogen is preferably added to give a partial pressure of hydrogen to hydrocarbon of 1.5 : 1 to 8.6 : 1. Before mixing the effluent from the methylcyclopentane isomerization stage is treated for the removal of hydrohalic acid and the effluent from the methyl pentane isomerization stage is treated for the removal of hydrogen.  In the fractionation at the product stage a ratio of normal hexane and/or methylcyclopentane to benzene of at least 10 to 1, preferably at least 15 to 1, by volume, is maintained because ratios below 10 to 1 render impossible an efficient separation of cyclohexane from benzene without an impractical loss of the former.  In an example, straight-run gasoline is fractionated to separate a hexane fraction of boling range 55 DEG  to 90 DEG  C., containing 20.5 per cent branched hexanes, 20 per cent n-hexane, 19 per cent methylcyclopentane, 35 per cent cyclohexane and 3.5 per cent benzene by volume and refractionated to separate a branched hexane fraction (A) of boiling range 55 DEG  to 65 DEG  C., containing 80 per cent branched hexanes, 16.7 per cent n-hexane and 1.3 per cent benzene, an intermediate fraction (B) boiling range 65 DEG  to 75 DEG  C., containing 39 per cent n-hexane, 9 per cent branched hexanes, 43.5 per cent methylcyclopentane and 8 per cent benzene, and as a bottoms product substantially all the cyclohexane, fraction (B) is isomerized by contact for 29 minutes with an aluminium chloride hydrocarbon complex catalyst at 80 DEG  C. in the presence of 0.9 per cent hydrogen chloride by weight of feed when 75 per cent of methylcyclopentane is converted to cyclohexane and 40 per cent of n-hexane to branched hexanes, fraction (A) is isomerized by contact for 80 seconds with a molybdenum sulphide catalyst at 400 DEG  C., 20 atmospheres pressure, in the presence of added hydrogen, a conversion of branched hexanes to n-hexane of 17 per cent being attained, the two effluents respectively freed from hydrogen chloride and hydrogen are then combined and fractionated in a product fractionator to produce a liquid fraction of cyclohexane and a vapour fraction of open-chain hexanes, methylcyclopentane and benzene which latter is refractionated to separate a vapour fraction comprising open-chain hexanes with less than 1.5 per cent of benzene from a liquid fraction comprising methylcyclopentane, open-chain hexanes and benzene, the vapour fraction being returned to the hexane isomerization zone whilst a portion of the liquid fraction is returned to the methylcyclopentane isomerization zone, liquid cyclohexane withdrawn from the product fractionator may be refractionated to produce cyclohexane containing less than 0.1 per cent of benzene.